21. Sets

A Set is an unordered collection that holds no duplicates. setOf builds a read-only set and silently drops repeated elements.

fun main() {
    val primes = setOf(2, 3, 5, 3, 2)   // duplicates removed
    println(primes)
    println(5 in primes)                // membership test

    val evens = mutableSetOf(2, 4)
    evens.add(6)
    evens.add(4)                        // already present, ignored
    println(evens)

    // sets support the usual mathematical operations
    val a = setOf(1, 2, 3)
    val b = setOf(3, 4, 5)
    println(a union b)                  // infix syntax
    println(a intersect b)
}

Running it:

$ kotlin run
[2, 3, 5]
true
[2, 4, 6]
[1, 2, 3, 4, 5]
[3]

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